The present invention relates to optical modules having photoelectric conversion functions to conduct optical communications. The present invention also relates to substrates for such optical modules as well as an optical coupling structure.
In response to the recent development of information and communication technologies (including the Internet) and the recent dramatic performance improvement of information processing equipment, there has been a growing need to transmit and receive a large capacity of data e.g. graphical data or video data. In order to carry out large-capacity data communications without restraint via an information network system, it is desirable that the information network system has a data transmission speed of several Gbps or higher. Optical communication technologies are expected to be especially useful to achieve such a high-speed data communication environment. There has also been a growing need to speed up short-distance signal communications between wiring boards of information processing equipment and between LSI chips of a wiring board. For these reasons, the shift from conventional data transmission using metal cables and/or metal wiring to optical transmission is desired.
In the optical transmission, optical elements (such as light-emitting elements and light-receiving elements) are generally used for conversion from optical signals to electrical signals and from electrical signals to optical signals. Further, optical waveguides (such as optical fibers) are used as data transmission media in the optical transmission. Various proposals have been made on the photoelectric conversion module, also called “optical module”, in which an optical element is supported on a module substrate and the optical coupling structure between an optical element and a fiber optic cable.
For instance, Japanese Laid-Open Patent Publication No. 2003-207694 proposes an optical coupling structure between an optical element and a multifiber optic cable on a wiring board. The proposed optical coupling structure includes a flat cable connector fixed at an end of the fiber optic cable, a flat package (as a connector receptacle) in which the optical element and LSI chips are incorporated, a clamp spring and guide pins. The cable connector is stacked on a surface of the package, and then, the connector and the package are fastened with the clamp spring and the guide pins in such a manner as to allow mating and unmating of these connection parts along a vertical direction of the wiring board. Upon mating of the package with the cable connector, the optical element is optically coupled to the fiber optic cable.
There is also proposed an optical connection part 903 of the type shown in FIG. 26, which is specifically designed to mate with a so-called MT (Mechanically Transferable) connector so as to provide an optical coupling between an optical element 902 and a multifiber optic cable 905, on “The Fifth Forum on Electronic SI Research, Feb. 26, 2004, Abstract, Page 86 (bottom section)”. The proposed optical connection part 903 is characterized as having a right-angle optical path conversion waveguide. The optical element 902 is face-up mounted on a wiring board 901 via bump contacts, and the MT connector has a plug 906 fixed to an end of the fiber optic cable 905. The optical connection part 903 is attached at a lower face thereof to an optical face of the optical element using an adhesive 904. The optical connection part 903 and the connector plug 906 are arranged with an end face of the optical connection part 903 abutting on an end face of the connector plug 906. Then, the optical connection part 903 and the connector plug 906 are fastened together with a clamp spring 907 in such a manner as to allow mating and unmating of these connection parts 903 and 906 along a lateral direction of the wiring board 901.
Japanese Laid-Open Patent Publication No. 2002-170965 proposes an optical module mounted on a printed circuit board and having an optical element supported on a silicon substrate. The silicon substrate has two opposite main surfaces: one main surface supporting thereon the optical element and the other main surface having positioning projections and depressions engaged with positioning projections and depressions of the printed circuit board so as to allow optical axis alignment of the optical element with an optical waveguide (such as an fiber optic cable).
Japanese Laid-Open patent Publication No. 2004-31743 proposes, although not directly related to an optical module, an electronic device in which an electronic component is mounted on a ceramic substrate. The ceramic substrate has two laminated ceramic substrate members joined together in such a manner that the direction of lamination of ceramic insulating layers in one substrate member is perpendicular to the direction of lamination of ceramic insulating layers in the other substrate member. The ceramic substrate also has a shield member interposed between two laminated substrate members so that the substrate members are electrically independent of each other. This substrate configuration is advantageous to achieve a low profile of the electronic device. It should be noted that the arrangement of an optical element on such a laminated ceramic substrate is neither disclosed nor suggested by Japanese Laid-Open Patent Publication No. 2004-31743.